Assay test kits are currently available for testing a wide variety of medical and environmental conditions or compounds, such as for testing for the existence of a hormone, a metabolite, a toxin, or a pathogen-derived antigen. Most commonly these tests are used to enable medical diagnostics in the home testing context, the point of care testing context, or the laboratory context. For example, lateral flow tests rely on a form of immunoassay in which the test sample flows along a solid substrate via capillary action. Some tests are designed to make a quantitative determination, but in many circumstances the tests are designed to return or indicate a positive/negative qualitative indication. Examples of assays which enable such qualitative analysis include blood typing, most types of urinalysis, pregnancy tests, and AIDS tests. For these tests, with proper illumination, a visually observable indicator such as the presence of agglutination or a color change may indicate the result of the test.
Such assay-based tests can generally be divided into two categories. A first category includes assay-based tests in which, after the test sample flows along the solid substrate as noted above, the results of the tests (such as the colored or visible lines resulting from the test) are displayed or made visible to a human interpreter of the test. For example, a home pregnancy test may display one or more lines, wherein the perception by the human interpreter of a designated quantity of lines (such as two lines) indicates a positive outcome of the test (e.g., that the person taking the test is pregnant). Such tests can be inexpensive, but can also result in operator error or uncertainty by the human interpreter of the tests.
A second category of assay-based tests are tests which can be read by one or more opto-electronic assay readers. In such situations, a conventional assay strip-based test is read and/or analyzed by one or more opto-electronic devices. Such opto-electronic devices may utilize an optical detection technique to determine the concentration of particular analytes on the assay strip. These opto-electronic readers can vary in terms of the technology utilized to detect the results of the test. Generally, however, these opto-electronic devices are more expensive than their human-interpretable counterparts.
A first type of opto-electronic reader can include imaging-based opto-electronic readers. In such imaging-based readers, an array of detectors, such as a camera or other image detector, captures an image of a two-dimensional portion of the assay strip. For example, an image detector may include a CMOS or CCD image sensor which includes at least one semiconductor having a plurality of circuits that convert detected light to voltages. In such image sensors, circuitry on a silicon chip converts the voltages indicative of detected light into digital data representative of the sensed image. The device then applies known image processing algorithms to the captured image to accommodate certain imaging artifacts, such as mechanical tolerance artifacts or spatial non-uniformity artifacts. After the algorithms are applied, the circuitry analyzes the sensed image and outputs data indicative of a result. Such devices can also be modified to perform multiplexed tests, wherein a plurality of different portions of the assay strip are analyzed in the same test, and a result is determined based on each of the analyzed portions of the strip.
Known imaging-based readers suffer from certain drawbacks. Specifically, the cost associated with the optical detector and the supporting electronics required to analyze the image captured by the optical detector, such as a micro-controller with image processing capability, can be relatively high, and can prevent broad implementations of a consumer-based product utilizing such opto-electronic readers.
A second type of opto-electronic reader can include photodiode based opto-electronic readers. In such readers, one or more detectors of the reader is implemented as a photodiode, such as a PIN-diode, in which the amount of electricity flowing through the diode varies proportionately to the amount of optical signal detected, are used to collect data indicative of a representation of the results of the test as indicated visually by the assay strip. Corresponding circuitry implements one or more algorithms to analyze the amount of electricity flowing in the PIN-diode, and thus outputs or otherwise indicates the results of the assay test.
Photodiode-based readers also suffer from certain similar drawbacks to those discussed above with respect to imagers. While the circuitry required to drive known photodiode-based readers may be simpler than the circuitry required to drive similar imagers, and such readers may therefore be more cost effective than corresponding imagers, known photodiode-based readers suffer from drawbacks relating to their lack of scalability. Particularly, photodiode-based readers do not provide spatial information. For example, certain known PIN-based readers cannot differentiate between a plurality of visible lines on an assay strip. Other photodiode-based readers can differentiate between (and monitor) a plurality of different analyte regions on an assay strip only by including a plurality of immovable detectors in the form of a plurality of photodiode-diodes, with one detector corresponding to each potentially detected line. The cost and logistical issues associated with incorporating a plurality of photodiode-diodes in a single reader can thus be disadvantageous. Moreover, an existing reader with a plurality of detectors, implemented as a plurality of photodiode-diodes, may be limited to only analyzing assay test strips that detect the presence of certain types of analytes based on the static positions of the analyte regions, and thus based on the static positions of the detectors.
One known photodiode-based reader is implemented as the Clearblue® digital pregnancy test kit, manufactured and sold by SPD Swiss Precision Diagnostic. In this embodiment, two separate detectors (specifically, two separate PIN-diode based detectors) are positioned adjacent to a position associated with a control line and a test line, The qualitative result of the test (i.e., whether the provider of the sample for the test is pregnant), is based on which of these lines are visible following applying biological fluid to the assay test strip. Thus, while a plurality of lines of an assay test strip can be detected, the device is limited to tests which have analyte regions corresponding to the fixed positions of the photodiode detectors. Additional test lines require additional photodiode detectors, and thus are associated with additional costs and require development of different reader components.
To overcome the limitations of known photodiode-based readers attributable to the inability of such readers to simultaneously monitor a plurality of different portions of an assay test strip, certain known readers implement a single detector mounted on an electro-mechanical scanning mechanism. During testing, the scanning mechanism moves the photodiode of the reader across a stationary assay strip and provides a profile of an optical response representing analyte reactions along a one-dimensional portion of that assay strip. Most high-end commercial systems available today that utilize photodiode to monitor a plurality of different analytes contained in a single assay strip rely on such electro-mechanical scanning technology, wherein the scanner is driven by a stepper motor or other appropriate type of motor. However, such systems also suffer from certain drawbacks relating to the scanning apparatus' reliance on the stepper-motor. Such systems can be large, making portability difficult, and can be expensive, with costs ranging from two-thousand dollars to three-thousand dollars and upward.
Thus, it is desirable to create a portable, low-cost, stand-alone assay test strip reader which utilizes a single detector (or array of detectors) to detect the presence of a plurality of different analyte regions on the assay test strip without regard for the pattern of the analyte regions on the assay test strip.